An experimental study is carried out of the effect on the propagation
of a smolder reaction through the interior of a porous fuel of a force
d flow of oxidizer opposing the direction of smolder propagation. The
potential effect of buoyancy in the process is also analyzed by conduc
ting the experiments in the upward and downward propagation, and compa
ring the respective results. The experiments are conducted with a high
void fraction flexible polyurethane foam as fuel and air as oxidizer,
in a geometry that approximately produces a one-dimensional smolder p
ropagation. Measurements are performed of the smolder reaction propaga
tion velocity and temperature as a function of the location in the sam
ple interior, the foam and air initial temperature, the direction of p
ropagation, and the air flow velocity. For both downward and upward sm
oldering three zones with distinct smolder characteristics are identif
ied along the foam sample. An initial zone near the igniter were the s
molder process is influenced by heat from the igniter, an intermediate
zone where smolder is free from external effects, and a third zone ne
ar the sample end that is affected by the external environment. The sm
older velocity data are correlated in terms of a nondimensional smolde
r velocity derived from a theoretical model of the process previously
developed. The analysis of the results confirm that the smolder proces
s is controlled by the competition between the supply of oxidizer and
the transfer of heat to and from the reaction zone. At low flow veloci
ties oxygen depletion is the dominant factor controlling the smolder p
rocess, and the smolder velocity and temperatures are relatively small
. Increasing the flow velocity strengthens the smolder reaction due to
the oxygen addition resulting in increased smolder velocities and tem
peratures. These parameters, however, reach a maximum and as the air v
elocity is increased further the smolder reaction becomes weaker and e
ventually dies out due to convective cooling.